High pressure and time resolved luminescence spectra of Gd3Ga5O12:Pr crystal

Luminescence spectra and time resolved luminescence spectra of GGG crystal doped with Pr³⁺ were measured at high hydrostatic pressure from ambient to 220 kbar. Effect of pressure results in the red shift of all luminescence lines related to Pr³⁺ ion emission equals from −0.32 to −1.02 cm⁻¹/kbar and in the diminishing of the luminescence lifetimes. The luminescence decay related to emission from ³P₀ state was single-exponential and diminished with pressure from 23 μs at ambient pressure to 6.5 μs at 165 kbar. Luminescence decay related to transition form ¹D₂ state was two-exponential with longer decay equal to 162 μs at ambient pressure and 120 μs at 165 kbar. We discussed effect of pressure on the ¹D₂ → ³H₄ luminescence and emission from ³P₀ state in the context of non-radiative processes that depopulate the ³P₀ and populate the ¹D₂ state, considering mainly multiphonon relaxation processes and depopulation via the praseodymium trapped exciton state.     

High pressure luminescence and time resolved spectra of La2Be2O5:Pr

We present luminescence, luminescence excitation and luminescence time resolved spectra of La₂Be₂O₅:Pr³⁺ system. We used high pressure spectroscopy approaches, with high pressure applied in diamond anvil cell (DAC) and sapphire anvil cell (SAC), for detailed analysis of luminescence related to the 4f5d → 4f² and 4f² → 4f² transitions. We present effect of up-converted luminescence related to 4f5d → 4f² transition excited with 488 nm. We also discussed possibility of existence of praseodymium trapped exciton (PTE) states in La₂Be₂O₅:Pr³⁺ system. Lack of the PTE is attributed to high quantity of bulk modulus of this material.     

Enhanced G4 emission in NaLaF4: Pr, Yb and charge transfer in NaLaF4: Ce, Yb studied by fourier transform luminescence spectroscopy

A high resolution luminescence study of NaLaF₄: 1%Pr³⁺, 5%Yb³⁺ and NaLaF₄: 1%Ce³⁺, 5%Yb³⁺ in the UV to NIR spectral range using a InGaAs detector and a fourier transform interferometer is reported. Although the Pr³⁺(³P₀ → ¹G₄), Yb³⁺(²F_7/2 → ²F_5/2) energy transfer step takes place, significant Pr³⁺¹G₄ emission around 993, 1330 and 1850 nm is observed. No experimental proof for the second energy transfer step in the down-conversion process between Pr³⁺ and Yb³⁺ can be given. In the case of NaLaF₄: Ce³⁺, Yb³⁺ it is concluded that the observed Yb³⁺ emission upon Ce³⁺ 5d excitation is the result of a charge transfer process instead of down-conversion.     

The influence of the Pr 4f5d configuration on the S0 emission efficiency and lifetime in LaPO4

The photoluminescence and excitation spectra of Pr³⁺ activated LaPO₄ has been investigated in the 1.6-300 K temperature region. At room temperature, the luminescence of LaPO₄:Pr³⁺ is composed of the interconfigurational 4f¹5d¹ → 4f² emission transitions. However, in the 1.6-60 K temperature range, the emission spectrum also consists of the intraconfigurational emission transitions that emanate from the ¹S₀ state. A radiative lifetime of 145 ns is measured for the Pr³⁺¹S₀ → ¹I₆ emission transition in LaPO₄. This is one of the shortest radiative lifetime observed for this transition in a solid. The energy position of the Pr³⁺¹S₀ state in LaPO₄ is established by high-resolution emission spectrum at 46 375 ± 5 cm⁻¹. A detailed analysis of the thermal quenching of the ¹S₀ lifetime and emission intensity is presented. It is proposed that the lowest energy state of the relaxed 4f¹5d¹ configuration is situated energetically below that of the ¹S₀ state.     

Red and infrared luminescence from tetragonal YSZ:Pr single crystal fibres grown by LFZ

Single crystal fibres of Pr³⁺-doped tetragonal yttria stabilized zirconia were grown by the laser floating zone method. The fibres show strong red luminescence at room temperature under ultraviolet optical pumping, which is due to the transition between the ¹D₂ and ³H₄ multiplets of the Pr³⁺ ion. Additionally, in the infrared spectral range main transitions were found at ∼1140 nm and 1560 nm. Their intensity ratio was shown to be dependent on the excitation wavelength, suggesting the presence of multiple Pr³⁺-related centres.     

Photoluminescence characteristics of Li-doped CaTiO3:Pr thin films grown on Si (100) substrate by PLD

The effects of Li-doped CaTiO₃:Pr³⁺ thin films have been investigated by varying the lithium ion concentrations from 0 to 5 wt.%. The films have been deposited on Si (100) substrate using a pulsed laser deposition technique. Structural properties of these films have been studied by the measurement of their XRD, SEM, and AFM. The variation of Li⁺ concentration influences the crystallinity and surface morphology of the CaTiO₃:Pr³⁺ thin films. As Li⁺ content increases from 0 to 1 wt.%, the crystallinity and intensity of emission increases. The dominant emission is from ¹D₂ → ³H₄ transition at 613 nm. The ¹D₂ emission quenching has also been observed in highly doped sample and is related to the cross-relaxation process between Pr³⁺ ions.     

Fast d-f emission in Ce, Pr and Nd activated RbCl

In the search for new scintillator materials, Ce³⁺ doped chlorides are a promising class of materials, combining a high efficiency and fast response time. Even shorter response times may be achieved by replacing Ce³⁺ by Pr³⁺ or Nd³⁺ as the lifetime of the d-f emission is substantially shorter for these ions. Here we report on the luminescence properties of Ce³⁺, Pr³⁺ and Nd³⁺ in RbCl and investigate the potential as a scintillator material. Under UV excitation Ce³⁺ shows d-f emission between 325 and 425 nm. The emission originates from multiple (differently charge compensated) Ce³⁺ sites. The luminescence lifetime varies with wavelength and is ∼40 ns for the longer wavelength emission. For RbCl:Pr³⁺ three d-f emission band are observed between 250 and 350 nm which can be assigned to transitions from the lowest energy fd state to different ³H_J (J = 4-6) states within the 4f² configuration of Pr³⁺. The decay time is ∼17 ns. For the Nd³⁺ activated sample a weak emission band around 220 nm is observed only at 8 K which may be due to d-f emission. The very short lifetime (4 ns) is faster than the radiative lifetime, indicating that the d-f emission is quenched by relaxation to lower lying 4f³ states or by the process of photoionization. Under VUV excitation at wavelengths below 175 nm (the bandgap of RbCl) the d-f emission is very weak for Ce³⁺, Pr³⁺ and Nd³⁺ doped RbCl and the emission spectra are dominated by defect related emission. This indicates that energy transfer from the host lattice to the fd states is inefficient which prevents application as a scintillator material.     

CaSc2O4:Eu: A tunable full-color emitting phosphor for white light emitting diodes

We report an intense full-color emission originating from ⁵D_0,1,2,3 to ⁷F_0,1,2,3,4 transitions of Eu³⁺ in CaSc₂O₄ upon 395 nm excitation. The emission spectra vary with increasing Eu³⁺ concentration, demonstrating tunable color coordinates from white to red region in the CIE chromaticity diagram. Considering the relaxation from ⁵D_J to ⁵D_J−1 through cross energy transfer, the Eu³⁺ concentration dependent emission spectra are well simulated based on the analysis of steady state rate equations and the measured lifetimes of the ⁵D_J levels. It is suggested that CaSc₂O₄:Eu³⁺ could be a potential single-phased full-color emitting phosphor for near-ultraviolet InGaN chip pumped white light emitting diodes.     

Photoluminescence and radioluminescence of pure and Ce activated Na3Gd(PO4)2

The spectroscopic properties of Na₃Gd(PO₄)₂ and Na₃Gd(PO₄)₂:Ce³⁺ phosphors in the VUV-UV spectral range were investigated. Five excitation bands of Ce³⁺ ions at Gd³⁺ sites are observed at wavelengths of 205, 246, 260, 292, and 321 nm. Doublet Ce³⁺ 5d → 4f emission bands are observed at 341 and 365 nm with a decay constant τ_1/e around 26 ns. The X-ray excited luminescence of Na₃Gd_0.99Ce_0.01(PO₄)₂ at room temperature shows a photon yield of ∼17,000 photons/MeV of absorbed X-ray energy.     

GeO2 dopant induced enhancement of red emission in CaAl12O19:Mn phosphor

In order to search efficient red-emitting phosphors for white LEDs application, CaAl₁₂O₁₉:Mn⁴⁺ phosphors have been prepared by a combustion method assisted with GeO₂ flux. The influence of GeO₂ concentration and annealing temperature on the structure and luminescence intensity for the phosphors has been investigated. The mechanism for luminescence enhancement has been discussed. At GeO₂ doping concentration of 1.5 mol%, the red emission intensity increases by 81% under 330 nm UVA excitation. More isolated luminescence center Mn⁴⁺ ions rather than pairs of Mn⁴⁺-Mn²⁺ ions are formed in the lattice with the introduction of GeO₂ at high temperature oxidation, leading to the enhancement of the red emission. A feasible new way to enhance the red emission in CaAl₁₂O₁₉:Mn⁴⁺ phosphor is obtained.     

A novel red phosphor NaLa4(SiO4)3F: Eu

A novel red phosphor NaLa₄(SiO₄)₃F: Eu³⁺ was synthesized by the conventional solid-state reaction at 950 °C for the first time. The luminescence properties of NaLa₄(SiO₄)₃F: Eu³⁺ were investigated, and the critical concentration of the activator concentration (Eu³⁺) was found to be 0.1 mol per formula unit. The phosphor presented red luminescence under the ultraviolet excitation of 254 or 395 nm, attributed to the transitions from ⁵D₀ excited states to ⁷F_J ( J = 0-4) ground states of Eu³⁺ ions. The results indicated that this newly-developed phosphor could find applications in tricolor fluorescent lamp, phosphor-liquid crystal displays and white lighting devices utilizing GaN-based excitation in the near UV.     

Luminescence enhancement of CaZnGe2O6:Tb afterglow phosphors synthesized using ZnO nanopowders

CaZnGe₂O₆:Tb³⁺ afterglow phosphors were prepared by solid state reaction using organic coated ZnO nanopowders and their photoluminescence, X-ray luminescence and afterglow properties were investigated. The CaZnGe₂O₆:Tb³⁺ samples emit a green luminescence at 548 nm attributed to the ⁵D₄-⁷F₅ transition of Tb³⁺. It was observed that the replacement of bulk ZnO by ZnO nanopowder in the sample synthesis increases the luminescence intensity. By adjusting the mass ratio of bulk ZnO to nanopowder ZnO, the photoluminescence intensity, X-ray luminescence intensity, and afterglow efficiency are improved. The optimized sample made with a 0.71 ratio of nano ZnO to bulk ZnO has a factor of four enhancement in X-ray luminescence, photoluminescence and afterglow intensities in comparison with the sample made with 100% bulk ZnO.     

Self-assembled 3D flower-like NaY(MoO4)2:Eu microarchitectures: Hydrothermal synthesis, formation mechanism and luminescence properties

Self-assembled 3D flower-like NaY(MoO₄)₂:Eu³⁺ microarchitectures were successfully synthesized by a glycine-assisted hydrothermal method at 180 °C. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) were employed to characterize the as-obtained products. It was found that morphology modulation could be easily realized by changing the time of hydrothermal reaction system. 3D flower-like NaY(MoO₄)₂:Eu³⁺ microarchitectures were formed with 72 h reaction time. The formation mechanism for flower-like architecture was proposed on the basis of a series of time-dependent experiments. The NaY(MoO₄)₂:Eu³⁺ powders obtained can be effectively excited by 396 nm light, and exhibit strong red emission around 615 nm, attributed to the Eu³⁺⁵D₀ → ⁷F₂ transition. An investigation on the photoluminescence (PL) properties of NaY(MoO₄)₂:Eu³⁺ obtained revealed that the luminescence properties were correlated with the morphology and size.     

Optical properties of transparent Dy doped Ba2TiSi2O8 glass ceramic

The Ba₂TiSi₂O₈ is a well known piezoelectric, ferroelectric and non-linear crystal. Nanocrystals of Ba₂TiSi₂O₈ doped with 1.5 Dy³⁺ have been obtained by thermal treatment of a precursor glass and their optical properties have been studied. X-ray diffraction patterns and optical measurements have been carried out on the precursor glass and glass ceramic samples. The emission spectra corresponding to the Dy³⁺: ⁴F_9/2 → ⁶H_13/2 (575 nm), ⁴F_9/2 → ⁶H_11/2 (670 nm) and ⁴F_9/2 → ⁶H_9/2 (757 nm) transitions have been obtained under laser excitation at 473 nm. These measurements confirm the incorporation of the Dy³⁺ ions into the Ba₂TiSi₂O₈ nanocrystals which produces an enhancement of luminescence at 575 nm. At this wavelength has been demonstrated a maximum optical amplification around 1.9 cm⁻¹ (∼8.2 dB/cm).     

Scintillation properties of Ce-doped LuLiF4 and LuScBO3

The crystals of 1 mol% Ce-doped LuLiF₄ (Ce:LLF) grown by the micro-pulling down (μ-PD) method and 1 mol% Ce-doped LuScBO₃ (Ce:LSBO) grown by the conventional Czochralski (Cz) method were examined for their scintillation properties. Ce:LLF and Ce:LSBO demonstrated ∼80% transparency at wavelengths longer than 300 and 400 nm, respectively. When excited by ²⁴¹Am α-ray to obtain radioactive luminescence spectra, Ce³⁺ 5d-4f emission peaks were detected at around 320 nm for Ce:LLF and at around 380 nm for Ce:LSBO. In Ce:LSBO, the host luminescence was also observed at 260 nm. By recording pulse height spectra under γ-ray irradiation, the absolute light yield of Ce:LLF and Ce:LSBO was measured to be 3600±400 and 4200±400 ph/MeV, respectively. Decay time kinetics was also investigated using a pulse X-ray equipped streak camera system. The main component of Ce:LLF was ∼320 ns and that of Ce:LSBO was ∼31 ns. In addition, the light yield non-proportionality and energy resolution against the γ-ray energy were evaluated.     

White light generation in Al2O3:Ce:Tb:Mn films deposited by ultrasonic spray pyrolysis

Aluminium oxide (Al₂O₃) films doped with CeCl₃, TbCl₃ and MnCl₂ were deposited at 300 °C with the ultrasonic spray pyrolysis technique. The films were analysed using the X-ray diffraction technique and they exhibited a very broad band without any indication of crystallinity, typical of amorphous materials. Sensitization of Tb³⁺ and Mn²⁺ ions by Ce³⁺ ions gives rise to blue, green and red simultaneous emission when the film activated by such ions is excited with UV radiation. The overall efficiency of such energy transfer results to be about 85% upon excitation at 312 nm. Energy transfer from Ce³⁺ to Tb³⁺ ions through an electric dipole-quadrupole interaction mechanism appears to be more probable than the electric dipole-dipole one. A strong white light emission for the Al₂O₃:Ce³⁺(1.3 at.%):Tb³⁺(0.2 at.%):Mn²⁺(0.3 at.%) film under UV excitation is observed. The high efficiency of energy transfer from Ce³⁺ to Tb³⁺ and Mn²⁺ ions, resulting in cold white light emission (x = 0.30 and y = 0.32 chromaticity coordinates) makes the Ce³⁺, Tb³⁺ and Mn²⁺ triply doped Al₂O₃ film an interesting material for the design of efficient UV pumped phosphors for white light generation.     

Dynamical processes of energy transfer in red emitting phosphor CaMoO4:Sm, Eu

Upon ⁴K_11/2 excitation of Sm³⁺ at 405 nm, the performance of energy transfer from Sm³⁺ to Eu³⁺ in the red emitting phosphor CaMoO₄:Eu³⁺, Sm³⁺ significantly extends its excitation region for better matching the near-UV LED. Photoluminescence spectra indicate that the energy transfer pathway concerns the relaxation from ⁴K_11/2 to ⁴G_5/2 of Sm³⁺ and subsequent transfer to ⁵D₀ of Eu³⁺ rather than ⁵D₁ of Eu³⁺. The fluorescent decay pattern of Sm³⁺⁴G_5/2 level in CaMoO₄:0.5% Sm³⁺, 2% Eu³⁺ is studied at 77 K based on the Inokuti-Hirayama formula, revealing an electronic dipole-dipole interaction between Sm³⁺ and Eu³⁺. The coefficient for the energy transfer is obtained to be 8.5 × 10⁻⁴⁰ s⁻¹ cm⁶. The fluorescence rise and decay pattern of Eu³⁺⁵D₀ level as Sm³⁺ is only excited at 77 K is well described by the dynamical processes of the energy transfer.     

Influence of excitation wavelengths on luminescent properties of Sr3Al2O6:Eu, Dy phosphors prepared by sol-gel-combustion processing

Eu²⁺ and Dy³⁺ ion co-doped Sr₃Al₂O₆ red-emitting long afterglow phosphor was synthesized by sol-gel-combustion methods using Sr(NO₃)₂, Al(NO₃)₃·9H₂O, Eu₂O₃, Dy₂O₃, H₃BO₃ and C₆H₈O₇·H₂O as raw materials. The crystalline structure of the phosphors were characterized by X-ray diffraction, luminescent properties of phosphors were analyzed by fluorescence spectrophotometer. The effect of excitation wavelengths on the luminescent properties of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors was discussed. The emission peak of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphor lays at 516 nm under the excitation of 360 nm, and at 612 nm under the excitation of 468 nm. The results reveal that the Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphor will emit a yellow-green light upon UV illumination, and a bright red light upon visible light illumination. The emission mechanism was discussed according to the effect of nephelauxetic and crystal field on the 4f⁶5d¹ → 4f⁷ transition of the Eu²⁺ ions in Sr₃Al₂O₆. The afterglow time of (Sr_0.94Eu_0.03Dy_0.03)₃ Al₂O₆ phosphors lasts for over 600s after the excited source was cut off.     

Synthesis and blue to near-infrared quantum cutting of Pr/Yb co-doped Li2TeO4 phosphors

Near-infrared (NIR) quantum cutting luminescent materials Li₂TeO₄ doped with Pr³⁺ and Yb³⁺ were synthesized by solid-state reaction method. The dependence of Yb³⁺ doping concentration on the visible- and NIR-emissions, decay lifetime, and quantum efficiencies of the phosphors are investigated. Quantum cutting down-conversion involving 647 nm red emission and 960-1050 nm broadband near-infrared emission for each 487 nm blue photon absorbed is realized successfully in the resulting phosphors, of which the process of near-infrared quantum cutting could be expressed as ³P₀(Pr³⁺) → ²F_5/2(Yb³⁺) + ²F_5/2(Yb³⁺). The maximum quantum cutting efficiency approaches up to 166.4% in Li₂TeO₄: 0.3 mol%Pr³⁺, 1.8 mol%Yb³⁺ sample corresponding to the 66.4% value of energy transfer efficiency.     

A red-emitting heavy doped phosphor Li6Y(BO3)3:Eu for white light-emitting diodes

A series of Eu³⁺ activated Li₆Y_1−xEu_x(BO₃)₃ (0.05 ? x ? 1) phosphors were synthesized by solid-state reaction method. The structures and photoluminescent properties of the phosphors were investigated at room temperature. The results of XRD patterns indicate that these phosphors are isotypic to the monoclinic Li₆Gd(BO₃)₃. The excitation spectra indicate that these phosphors can be effectively excited by near UV (370-410 nm) light. The red emission from transition ⁵D₀→⁷F₂ is dominant. The emission spectra exhibit strong red performance (CIE chromaticity coordinates: x = 0.65, y = 0.35), which is due to the ⁵D₀−⁷F_J transitions of Eu³⁺ ions. The relationship between the structure and the photoluminescent properties of the phosphors was studied. The concentration quenching occurs at x ≈ 0.85 under near UV excitation. Li₆Y(BO₃)₃:Eu³⁺ has potential application as a phosphor for white light-emitting diodes.